1. Field of the Invention
The present invention relates generally to an improved electroerosion discharge machine ("EDM"). More particularly, this invention utilizes several wires, which are electrically insulated from one another and may be electrically charged with varying parameters to permit the electroerosion of several workpieces, made of different substances and thickness, simultaneously.
2. Description of the Prior Art
The concept of electrical discharge machining is a process using nonstationary, time-spaced electrical discharges between an electrode and a workpiece for the removal of material. By employing electrical discharge machining, it is possible to cut, or otherwise mode, intricate shapes into all conductive materials with an extremely high level of precision.
Standard EDM equipment has been used in industry for over three decades and generally employs a graphite contoured, or similar electrode to penetrate the desired workpieces. By providing a voltage between the electrode and workpiece and a servo system to control the gap, sparks are induced in the gap which results in vaporizing the workpiece and eventually creating a shape which is the inverse image of the electrode.
The prior art also includes the concept of wire EDM. This form of electrical discharge machining involves use of an electrode that is a continuously moving, expendable wire which conducts electricity to the workpiece without actually touching the workpiece. The wire is generally made of either copper, brass, molybdenum or tungsten having usually a diameter of 0.002 inches to 0.012 inches. The diameter of the wire may be reduced as it is used to erode the workpiece. Accordingly, the wire is often discharged as scrap once it has served its function in the EDM process.
To prevent short circuits between the workpiece and the electrode and to cool the wire, a dielectric fluid, e.g., de-ionized water, or other dielectric is employed to flush away the condensed material (debris).
Prior art devices have recognized that by varying the diameter of the wire used, the speed with which the wire erodes the workpiece by passing near it, the current passing through the wire and proper choice of polarity, different workpieces made out of various materials and having varying thicknesses may be accurately cut and shaped.
Wire EDM devices heretofore known have generally employed a single wire electrode to electrically erode a single workpiece. More recently, devices have become known which employ multiple wire electrodes to simultaneously erode with identical voltage, current and polarity. One such device is disclosed in U.S. Pat. No. 4,243,864, issued to Vieau et. al., on Jan. 6, 1981. Specifically, the device of the foregoing patent provides a plurality of supply spools of electrically conductive wire. Each of the spools provides a wire to a tension assembly from which the wire is delivered to a cutting guide assembly. The cutting guide assembly holds the wires parallel to each other so that identical workpieces receive multiple cuts simultaneously. In the prior art device, the used wires are then taken up by a take-up assembly. At the take-up assembly, the wires are wound onto a single take-up spool, providing the same electrical potential to all wires.
A major drawback in the prior art device disclosed in U.S. Pat. No. 4,243,864, as well as in other devices known to the art is the inability of a multiple wire electrode EDM device to simultaneously erode various workpieces made of different materials and different thicknesses said drawbacks being overcome by the present invention as more fully described hereinafter.